AnthonyL wrote :
What would suit us is a small tank above the kitchen warmed by the CH
system and maybe a thermostatically controlled element. At a previous
property a similar arrangement worked well from an open coal fired CH
system. Do such systems exist?

I understand you can buy an electrically heated local system (to where
it is consumed), which stores the combi heated water keeping it hot.
Thus you get hot water quickly, without the usual delay of a combi.